What on earth is that?

A RARE sight floated across the Halifax skyline yesterday, stunning those who saw it.

What looked like the doomed airship Hindenburg is in fact known as a lenticular cloud.

It is caused by blustery conditions at high altitudes.

The clouds often form around mountains and usually align themselves perpendicular to the direction of the wind.

But, as in this case, they can form where no mountains exist.

Layers of clouds stack one on the other, and the wind tends to “round off” the front and rear edges of the formation.

Yesterday’s cloud was made all the more spectacular because the clear blue skies made a stunning backdrop. Many Courier readers reported whole “convoys” of clouds, one following another, following another.

Lenticular clouds are often mistaken for UFOs due to their characteristic appearance and smooth, saucer-like shape.

According to Wikipedia, where stable moist air flows over high ground a series of large-scale standing waves may form on the downwind side.

“If the temperature at the crest of the wave drops to the dew point, moisture in the air may condense to form lenticular clouds.”

Dermod Quirk, of Savile Park, Halifax, said: “I have never seen anything like it in my life.” And Kelly Kilduff, responding on the Courier website, said: “I saw the cloud half an hour ago – so strange!”